I’d like to build a class D guitar amp. I know this has been discussed before, but I haven’t found the answers to my questions. Some background:
- The aim is approximately 100 watts output power (@ 8 ohm).
- I know overdriven solid states sound awful, so the guitar amp tone and overdrive will come from the preamp.
- It will be combined with whatever cabinet available, which in practice means it needs to handle 4-16 ohm speakers.
- I think good candidates could be TDA7498 and TDA8950 (or 54), for which pre-assembled boards are readily available.
So,
1. Are there better amps (than the aforementioned chips) for this?
2. Apart from different output powers and the potential need for output filter adjustment, is there a problem with hooking up the amps to speakers with different impedances (4-16 ohm)?
3. I’m planning to include a switch to select between to sets of inductors and capacitors for the output filter. Is that a bad idea? Is it necessary?
4. If the chip is designed for stereo, is it OK it leave one channel unconnected (input as well as output)?
Thanks in advance!
- The aim is approximately 100 watts output power (@ 8 ohm).
- I know overdriven solid states sound awful, so the guitar amp tone and overdrive will come from the preamp.
- It will be combined with whatever cabinet available, which in practice means it needs to handle 4-16 ohm speakers.
- I think good candidates could be TDA7498 and TDA8950 (or 54), for which pre-assembled boards are readily available.
So,
1. Are there better amps (than the aforementioned chips) for this?
2. Apart from different output powers and the potential need for output filter adjustment, is there a problem with hooking up the amps to speakers with different impedances (4-16 ohm)?
3. I’m planning to include a switch to select between to sets of inductors and capacitors for the output filter. Is that a bad idea? Is it necessary?
4. If the chip is designed for stereo, is it OK it leave one channel unconnected (input as well as output)?
Thanks in advance!
My first question is, especially for guitar (ie. not bass), do you really NEED 100W?
Let's keep in mind that guitar speakers, even in singles, have efficiencies in the mid-to-upper half of the 90dB @ 1W area. I guess the question is, how many people do you want to annoy, and how much?
For what it's worth, my band's guitarist, with a little TPA3118-based amp that i put together (powered with a 19v power brick, resulting in ~40w "clean"), got an Ibanez 4x12 4ohm cab up to about 117dB at around 2m in front of the cab, at full blast. That was pretty effin' LOUD despite wearing moulded earplugs. The master volume around half-way was enough to keep up with the drums right next to it.
Stereo chips can usually be configured as PBTL (in most cases, anyway).
Let's keep in mind that guitar speakers, even in singles, have efficiencies in the mid-to-upper half of the 90dB @ 1W area. I guess the question is, how many people do you want to annoy, and how much?
For what it's worth, my band's guitarist, with a little TPA3118-based amp that i put together (powered with a 19v power brick, resulting in ~40w "clean"), got an Ibanez 4x12 4ohm cab up to about 117dB at around 2m in front of the cab, at full blast. That was pretty effin' LOUD despite wearing moulded earplugs. The master volume around half-way was enough to keep up with the drums right next to it.
Stereo chips can usually be configured as PBTL (in most cases, anyway).
Khron and voltwide are very competent with guitar use.
TDA7498E or TDA8954 may be good candidates. TPA3116 can be sufficient.
In principle an output filter is optimized for the speaker impedance. But, if you use a filter for 8 Ohm and actually use a 4 Ohm speaker the filter will just be damped a little more. Make sure the chokes can handle the 4 Ohm current. With 16 Ohm the filter will be a little less damped. You will hardly hear the difference.
Two different sets of filters will require very reliable connections because loosing the load on an active class D amplifier may cause damage.
You may leave one channel unused but only with a dummy load at the output of the filter or with that filter disconnected from the chip output.
TDA7498E or TDA8954 may be good candidates. TPA3116 can be sufficient.
In principle an output filter is optimized for the speaker impedance. But, if you use a filter for 8 Ohm and actually use a 4 Ohm speaker the filter will just be damped a little more. Make sure the chokes can handle the 4 Ohm current. With 16 Ohm the filter will be a little less damped. You will hardly hear the difference.
Two different sets of filters will require very reliable connections because loosing the load on an active class D amplifier may cause damage.
You may leave one channel unused but only with a dummy load at the output of the filter or with that filter disconnected from the chip output.
1. I do not expect significant sound differences between class-d-chips. Select them according to your power requirements and the losses they produce. Chose operating voltage depending on max power and impedance. For instance 36V for 80W/8Ohms, 24V for 40W/8Ohms, 12V for 10W/8Ohms.
Over the years I decided there is no need for 100W guitar amps for me and now I use most of the time 24V/8Ohm with TPA3118.
For smaller venues 16V (4xLiIon) 4 Ohm with a 6.5" Jensen MOD15.
Over the years I decided there is no need for 100W guitar amps for me and now I use most of the time 24V/8Ohm with TPA3118.
For smaller venues 16V (4xLiIon) 4 Ohm with a 6.5" Jensen MOD15.
Thread moved to I&A forum.Thank you so much for your input!
@Khron. Do I need 100 W? Very good question! Honestly, I don't know. I'm actually building this for a friend who's gonna use it for playing live at small venues (which is rather undefined. We decided to go for 100w which would give some power and headroom even at 16 ohm. But maybe the Tpa3116/18 is enough. I'll think about it.
Thanks again and sorry for posting on the wrong forum.
@Khron. Do I need 100 W? Very good question! Honestly, I don't know. I'm actually building this for a friend who's gonna use it for playing live at small venues (which is rather undefined
. We decided to go for 100w which would give some power and headroom even at 16 ohm. But maybe the Tpa3116/18 is enough. I'll think about it. Thanks again and sorry for posting on the wrong forum.
"Back in the day", people like Pete Townshend (of The Who) began to need those amounts of power because there wasn't yet much concept of what's PA today. And what with playing in bigger venues, they needed the SPL to cover the larger crowds.
Nowadays though, even in small(er) clubs, you might have your cab mic'd up and put through the PA, so "worst case" you need a bit of volume (and thus, power) just for some amount of monitoring.
My aforementioned bandmate got himself a 120W Laney Ironheart head a couple years back, but recently bought himself the 15W version, and even that's more than plenty loud for rehearsals, with that same 4x12. Just sayin'
Nowadays though, even in small(er) clubs, you might have your cab mic'd up and put through the PA, so "worst case" you need a bit of volume (and thus, power) just for some amount of monitoring.
My aforementioned bandmate got himself a 120W Laney Ironheart head a couple years back, but recently bought himself the 15W version, and even that's more than plenty loud for rehearsals, with that same 4x12. Just sayin'
Should be no problem. You may short circuit the input of the idle channel.
Better you configure the stereo amp in parallel BTL-mode, that reduces losses and spreads heat dissipation on both channels.
True guitarists always need more power. At least, they think they do.
I have a nominally 15-watt '65 Princeton Reverb reissue valve guitar amp that I have never managed to turn up to full volume, because it's too @$!~% loud.
I now live in an apartment, and I have a 2-watt valve guitar amp I built for use at home, and it's too loud - I ended up using it at jams, not at home.
Most recently I built a little single-ended amp with an estimated power output of 200 mW - 250 mW (one fifth to one fourth of a watt). That's about right for playing guitar in my apartment during the day, but connected to the stock Eminence speaker in my 'Princeton, it's too loud to overdrive at night.
If you had been building a 100 W valve guitar amp rather than, say, a 20 watt one, there would be considerable penalties to deal with: the 100 W amp would cost far more, and weigh far more, than the 20 W version.
The good news is that, using a modern solid state class D power amp, and a modern switching power supply, you don't suffer a huge weight or cost penalty for the unnecessary 80-odd watts.
A MI manufacturer called Matrix Amplification has already run with the same idea. Here is one of their guitar amps,with valves in the preamp and a 420 watt class-D power amp: Vintage British 800
-Gnobuddy
Reliable connections for multiple filters?
Not from my experience. A few years back, our workshop received a warranty repair; a German 1kW class D amplifier, the customer complaint was that "it did not sound right".
On switching it on, the workshop radio died. At the same moment, Steve, the radio mic technician popped his head around the door to ask who had just fired up a high powered transmitter.
The fault was dry joints on the output filter inductors and capacitors; the amplifier was fine.
Kevin
Not from my experience. A few years back, our workshop received a warranty repair; a German 1kW class D amplifier, the customer complaint was that "it did not sound right".
On switching it on, the workshop radio died. At the same moment, Steve, the radio mic technician popped his head around the door to ask who had just fired up a high powered transmitter.
The fault was dry joints on the output filter inductors and capacitors; the amplifier was fine.
Kevin
Thanks for the information!
I'm not too worried about the switch. I'm quite experienced in soldering (I build guitar effects) and I would etch daughter a pcb for the filters. But the agian, if the switch fails... Anyway, it seems like it's overkill.
Just to confirm; as suggested by FauxFrench, would just desoldering the components of the filter of one channel be safe for a mono application? Instead of a dummy load that is.
It seems to be what they do with the mono chip TDA7498MV (isn't that a special application of the TDA7498 rather than a separate chip?).
I'm not too worried about the switch. I'm quite experienced in soldering (I build guitar effects) and I would etch daughter a pcb for the filters. But the agian, if the switch fails... Anyway, it seems like it's overkill.
Just to confirm; as suggested by FauxFrench, would just desoldering the components of the filter of one channel be safe for a mono application? Instead of a dummy load that is.
It seems to be what they do with the mono chip TDA7498MV (isn't that a special application of the TDA7498 rather than a separate chip?).
Most likely, quality control at the fabrication plant catch some chips that happen to have one dead channel. Those will be marked differently, and sold as "mono" amplifiers.I wonder if a separate production process for a mono chip can be justified economically...
Years ago, I was told that much the same thing was true of Intel CPUs labelled and sold with varying clock speeds. During testing, the ones that happened to work at the highest clock speeds were separated, and their prices marked up substantially. Die hard gamers were willing to pay a lot more for the fastest CPU they could get their hands on.
-Gnobuddy
Most likely, quality control at the fabrication plant catch some chips that happen to have one dead channel. Those will be marked differently, and sold as "mono" amplifiers.
You're probably right! And the same goes for the low(er) power TDA7498L.
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